test(health): add degradation test for missing phasesDir (#1973)

Covers the behavior change from independent per-check degradation to
coupled degradation when the hoisted readdirSync throws. Asserts that
cmdValidateHealth completes without throwing and emits zero phase
directory warnings (W005, W006, W007, W009, I001) when phasesDir
doesn't exist.

Review feedback on #2053 from @trek-e.

tests/verify-health.test.cjs

@@ -767,3 +767,47 @@ describe('validate health --repair command', () => {
     assert.strictEqual(output.repairable_count, 0, `Expected no repairable issues for W002: ${JSON.stringify(output)}`);
   });
 });
+
+// ─────────────────────────────────────────────────────────────────────────────
+// Graceful degradation when phasesDir is missing (#1973)
+// ─────────────────────────────────────────────────────────────────────────────
+
+describe('validate health — missing phasesDir', () => {
+  let tmpDir;
+
+  beforeEach(() => {
+    tmpDir = createTempProject();
+  });
+
+  afterEach(() => {
+    cleanup(tmpDir);
+  });
+
+  test('completes without throwing and emits zero phase-directory warnings when phasesDir does not exist', () => {
+    // Setup: valid PROJECT, ROADMAP, STATE, config but NO phases directory
+    writeMinimalProjectMd(tmpDir);
+    writeMinimalRoadmap(tmpDir, ['1', '2']);
+    writeMinimalStateMd(tmpDir);
+    writeValidConfigJson(tmpDir);
+
+    // Remove the phases directory if it exists
+    const phasesDir = path.join(tmpDir, '.planning', 'phases');
+    if (fs.existsSync(phasesDir)) {
+      fs.rmSync(phasesDir, { recursive: true, force: true });
+    }
+
+    // Should complete without throwing
+    const result = runGsdTools('validate health', tmpDir);
+    assert.ok(result.success, `Command should succeed when phasesDir is missing: ${result.error}`);
+
+    const output = JSON.parse(result.output);
+
+    // Assert no phase-directory warnings fired
+    const phaseDirCodes = ['W005', 'W006', 'W007', 'W009', 'I001'];
+    const issues = output.issues || [];
+    for (const code of phaseDirCodes) {
+      const matches = issues.filter(i => i.code === code);
+      assert.strictEqual(matches.length, 0, `Expected no ${code} issues when phasesDir is missing, got: ${JSON.stringify(matches)}`);
+    }
+  });
+});